Downhole actuation ball, methods and apparatus

ABSTRACT

An actuation ball for a downhole tool, the actuation ball includes a ball body having an outer surface defining a seating surface with a substantially circular shape in section encircling an axis of the actuation ball; and a flexible protrusion attached to the ball body and extending substantially coaxially relative to the seating surface. Another actuation ball for a downhole tool, the actuation ball includes a body having an outer surface defining a seating surface, the body having a specific gravity less than 2.6.

This application claims priority from U.S. Ser. No. 61/545,860, filed Oct. 11, 2011.

FIELD

The present invention relates to downhole tools and, in particular, a downhole actuation ball for driving downhole tools. Apparatus and methods employing the actuation ball are also described.

BACKGROUND

Actuation balls are used to drive downhole tools. For example, actuation balls may be launched to drive a hydraulic sleeve. Hydraulic sleeves are used in various tools and include an annular seat on the sleeve that is formed to accept and catch a suitably sized ball thereon. When a ball lands thereon, a seal is formed between the ball and the sleeve that inhibits fluid flow therepast such that a hydraulic pressure can be built up above the ball, such hydraulic pressure being suitable to move the sleeve along the tubular in which it is installed. One possible sleeve and ball system is described in U.S. Pat. No. 6,907,936 of Jun. 21, 2005 to the assignee of the present application.

SUMMARY

In accordance with a broad aspect of the present invention, there is provided an actuation ball for a downhole tool, the actuation ball comprising: a body having an outer surface defining a seating surface, the body having a specific gravity less than 2.6.

In accordance with another broad aspect of the present invention, there is provided a downhole tool assembly comprising: a tubular body; a sliding sleeve valve positioned within and axially moveable along a length of the tubular body, the sliding sleeve valve including a valve seat; and an actuation ball having an outer surface defining a seating surface, the actuation ball having a specific gravity less than 2.6.

In accordance with another broad aspect of the present invention, there is provided a method for operating a downhole tool, the method comprising: providing a downhole tool including a tubular body and a sliding sleeve valve positioned within and axially moveable along a length of the tubular body, the sliding sleeve valve including a valve seat; providing an actuation ball having an outer surface defining a seating surface, the actuation ball having a specific gravity less than 2.6; positioning the downhole tool within a wellbore; launching the actuation ball from above the downhole tool such that the actuation ball moves to land in the valve seat of the sliding sleeve valve; driving the sliding sleeve valve to operate the downhole tool; and allowing circulation of the fluids in the wellbore to lift the actuation ball off the valve seat.

In accordance with another broad aspect of the present invention, there is provided an actuation ball for a downhole tool, the actuation ball comprising: a ball body having an outer surface defining a seating surface with a substantially circular shape in section encircling an axis of the actuation ball; and a flexible protrusion attached to the ball body and extending substantially coaxially relative to the seating surface.

In accordance with another broad aspect of the present invention, there is provided a downhole tool assembly comprising: a tubular body; a sliding sleeve valve positioned within and axially moveable along a length of the tubular body, the sliding sleeve valve including a valve seat; an inner bore defined by an inner wall of the tubular body and of the sliding sleeve valve; and an actuation ball including a ball body and a flexible protrusion, the ball body having an outer surface defining a seating surface with a substantially circular shape in section encircling an axis of the actuation ball, and the flexible protrusion extending from the ball body substantially coaxially relative to the seating surface, the flexible protrusion acting to orient the seating surface to land in the valve seat.

In accordance with another broad aspect of the present invention, there is provided a method for operating a downhole tool, the method comprising: providing a downhole tool including a tubular body; a sliding sleeve valve positioned within and axially moveable along a length of the tubular body, the sliding sleeve valve including a valve seat; and an inner bore defined by an inner wall of the tubular body and of the sliding sleeve valve; providing an actuation ball including a ball body and a flexible protrusion, the ball body having an outer surface defining a seating surface with a substantially circular shape in section encircling an axis of the actuation ball, and the flexible protrusion extending from the ball body substantially coaxially relative to the seating surface; launching the actuation ball from above the downhole tool such that the actuation ball moves through the inner bore and the ball body lands in the valve seat of the sliding sleeve valve, the protrusion acting to orient the seating surface to land in the valve seat; and driving the sliding sleeve valve to operate the downhole tool.

It is to be understood that other aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein various embodiments of the invention are shown and described by way of illustration. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modification in various other respects, all within the present invention. Accordingly the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings, several aspects of the present invention are illustrated by way of example, and not by way of limitation, in detail in the figures, wherein:

FIG. 1 is a sectional view through a downhole tool assembly according to another aspect of the present invention.

FIG. 2 is a sectional view along a center axis of an actuation ball according to one aspect of the invention.

FIGS. 3 a and 3 b are perspective views of parts of an actuation ball, according to another aspect of the present invention.

FIG. 4 is a sectional view along a center axis of an actuation ball according to another aspect of the invention.

FIGS. 5 a and 5 b are sectional views, shown exploded and assembled, respectively, of an actuation ball according to another aspect of the invention. These Figures are sometimes referred to collectively as FIG. 5.

FIGS. 6 a and 6 b are sectional views, shown exploded and assembled, respectively, of an actuation ball according to another aspect of the invention. These Figures are sometimes referred to collectively as FIG. 6.

FIG. 7 a is a perspective view of a ball body skeleton and FIG. 7 b is a perspective view of an assembled ball employing the skeleton of FIG. 7 a. These Figures are sometimes referred to collectively as FIG. 7.

FIG. 8 a is a sectional view of a ball and FIG. 8 b a sectional view through a downhole tool assembly with a ball of FIG. 8 a landed therein. These Figures are sometimes referred to collectively as FIG. 8.

DESCRIPTION OF VARIOUS EMBODIMENTS

The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.

An actuation ball, also called a plug, is a component of a downhole tool assembly. The actuation ball may take many different forms, but is conveyed to actuate a downhole tool. Generally, the downhole tool has a seating surface against which the ball lands, solidly or temporarily, to create a seal in the tool so that it can be actuated, for example by hydraulic pressure. The many different forms of actuation balls may include structures that are traditionally “ball” shaped, or structures shaped irregularly but capable of seating in the tool. The ball body itself may be irregular and/or the ball body may have an attachment connected thereto. Herein, all of these structures are defined as actuation balls.

One possible downhole tool assembly is shown in FIG. 1. A downhole tool assembly includes a ball 12 and a tool including a tubular body 14 and a sliding sleeve valve 18 positioned within and axially moveable along a length of the tubular body. Sliding sleeve valve 18 includes a valve seat 20 sized to catch ball 12. Valve seat 20 can take various forms. For example, the valve seat may include (i) a ball stop protruding into the inner diameter of the tubular body that catches ball 12 but allows some flow therepast, (ii) a ball stop that catches the ball and holds it in a sealing position against an adjacent sealing annular area, (iii) a structure that is fixed or a structure that is eventually overcome to let the ball pass, or (iv) a combined ball stop and sealing surface. In the illustrated embodiment, sliding sleeve valve 18 includes a valve seat that is a combined ball stop and sealing surface. Valve seat 20 is formed on an inner facing wall 18 a defining a bore through sleeve 18 from end to end and an upper portion of the inner facing wall has a tapering inner diameter to form valve seat 20 which is an inclined seating surface formed to catch and seal with actuation ball 12. The seat is often circular in orthogonal section from the sleeve's long axis x_(s). Thus, the seat often has a generally frustoconical surface with an inner diameter tapering from its upper end to its lower end. Valve seat 20 and ball 12 are correspondingly sized (i.e. the diameter of the ball, D ball, corresponds with the inner diameter at the seat) such that the ball can land on and create a seal against the seat.

Tubular body 14 can be formed to be installable in downhole strings such as liners, casing, production strings, well treatment strings, etc. For example, in the illustrated embodiment, the tubular body has its upper end 14 a and its lower end 14 b formed with threads such as threaded pins and boxes for threaded engagement to adjacent tubulars.

The form of the tubular body can depend on the function of the tool. In the illustrated embodiment, tubular body 14 includes ports 22 through which fluid can pass between the inner bore and outer surface 14 c of the tubular body. Ports 22 are opened and closed by movement of sleeve valve 18. Sleeve valve 18 can be moved by landing ball 12 in its seat 20. Sleeve valve 18 may be secured by releasable holding devices such as shear pins 24, lock rings, etc., which can be overcome if a certain force is applied thereto. In FIG. 1, shear pins 24 are shown already sheared from their locking position in gland 25 of sleeve 18.

When ball 12 lands in its seat, a piston is created on sleeve valve 18 through the sealing of the ball against the seat and pressure P can be built up above the piston to create a pressure differential across the piston, which drives the sleeve down to the lower pressure side.

Any holding devices such as pins 24 are overcome when a suitable differential is reached.

Ball 12 must therefore be durable and capable of withstanding at least the force to move the sleeve. It is desirable for the ball to be removed from the seat after the sleeve is moved. Extrusion of ball 12 through the sleeve, which may jam the ball in the seat should be avoided. In one embodiment, the ball has a low specific gravity such that it tends to lift upwardly off the seat after the pressure differential holding it in the seat is dissipated.

In another embodiment, the ball is selected to land in a particular orientation on the seat so that the ball seating area can be configured to suitably land and seal against the sealing area of the seat, while the remainder of the ball body may not meet these requirements. For example, the remainder of the ball body may be formed of less durable materials, may be angular, may have holes in the surface thereof.

In FIGS. 2 to 7, various embodiments of wellbore actuation balls are shown according to various aspects of the present invention.

The illustrated balls each include an outer surface that defines a seating surface on which the ball seals against the seat. The seating surface is shaped to seal against the valve seat 20. Since valve seats are often circular, the seating surface often has a substantially circular shape through a section orthogonal to an axis x of the ball (i.e. the circular shape encircles the axis). The seating area may, therefore, be cylindrical, conical or substantially spherical in shape. Some balls are substantially entirely spherical (FIGS. 1 to 7) and the seating surface in that case may be any area on the ball's outer surface. In other balls (FIG. 8 a), the outer surface is not entirely spherical or the construction of the ball is such that only certain areas of the ball's outer surface can accommodate seating, thus, those balls may have only a portion of their outer surface that is capable of acting as a seating surface. Balls having a generally spherical outer surface will advance through the string by rolling as well as being pumped down the well.

According to one aspect of the invention, the actuation ball is selected to have a specific gravity of less than 2.6 and in one embodiment a specific gravity of 1.2 to 1.5. In one embodiment, the actuation ball may be selected to include a specific gravity of 1.3 to 1.4 or about 1.35.

In one embodiment, a ball may be formed entirely of material that has a specific gravity of less than 2.6. However, if such a ball tends to be incapable of properly withstanding wellbore conditions (i.e. extruding, crushing, failing to create a seal, failing to actuate the target tools, etc.), it may be desirable to employ a combination of (i) materials that are durable and (ii) materials that lower the specific gravity of the ball and reduce milling time, if a ball becomes stuck.

In these embodiments, the balls may be formed of more than one material, one for strength and the other for low specific gravity. For example, one material, termed herein a body material, may include ceramic, polymer or metal, such as steel or aluminum, and may be used for strength, and the other material, term herein filler, may be employed to make the ball lighter and to reduce milling time. For the body material, ceramic, polymers, etc. may have specific gravities lower than 2.6 and may have the strength to withstand actuation pressures substantially without detrimental damage thereto. For example, some composites may have specific gravities in the order of 0.95. Aluminum may be used for strength and its relatively low specific gravity (2.6) in relation to other metals and non-metals.

For example, with reference to ball 12 of FIGS. 2, 3 a and 3 b, it has a specific gravity of less than 2.6 and has a body 30 formed of body material and at least one cavity 32, defined within cavity walls 34. The one or more cavities are filled with a filler having a lower specific gravity than the body material. The specific gravity can be achieved by consideration as to the body material used and the volume and the characteristics of the filler used to fill the one or more cavities.

The material employed to form body 30 can be selected from various durable materials capable of withstanding downhole conditions such as may include, for example, ceramics, aluminum, steel, titanium, one or more of polymers, such as phenolics, etc. The body materials may further include coatings, reinforcements, etc. Aluminum may be used for strength and relatively low specific gravity (2.6) in relation to other metals and non-metals.

Cavity 32 can be shaped in various ways. In the illustrated embodiment of FIG. 2, the ball contains a single cavity 32, but other embodiments may include a plurality of cavities. Ball 12 of FIGS. 2, 3 a, 3 b has cavity walls 34 shaped to define cavity 32 as an annular space. Directional changes in the cavity walls may be gradual rather than abrupt, such that stress cracking is minimized. However, some construction methods may leave some sharp corners and they will be accommodated. Other balls may have honeycomb cavities, cavities formed by bubbles, etc.

The one or more cavities may be filled with a solid or a fluid (i.e. including liquids and gases) that has a lower specific gravity than the body material such that overall the ball has a specific gravity of less than 2.6. For example, a filler gas such as air, helium or nitrogen, may be used. The gas may be at ambient, surface pressures, or at increased or reduced pressures relative to ambient, surface pressures. In one embodiment, a gas filler can be employed that is pressurized relative to ambient, surface pressures such that it acts against collapse stresses. In other embodiments such as shown in FIGS. 5 and 6, a solid filler 337, 437 such as a polymer, metal, composite, etc. can be used. These solid fillers may be selected to have a low specific gravity such as less than 2 and in one embodiment may be in the range of 0.5 to 1.5. In one embodiment, a polytetrafluoroethylene (PTFE, available for example as Teflon™ from Dupont Co.), with or without reinforcements such as glass fibers, may be employed as a filler.

Various constructions are possible. In some embodiments, such as those illustrated herein, the ball includes a multi-part construction. Such a construction facilitates manufacture, as the cavities can be formed directly and with intent in the materials of the ball parts. In one such embodiment, for example, ball 12 includes half sections 36 a, 36 b each formed to be partly-spherical on one surface, the outer facing surface 12 a, and on an opposite facing surface of each half section is formed with hollowed out regions of cavity walls 34. If the cavities are gas or liquid filled or have another filler that is displaceable, or harmed, by contact with the well fluids, a seal may be installed between the parts to protect against infiltration of fluids to the cavities and/or to protect against leakage of fluids from the cavities. For example, in the illustrated embodiment, an o-ring 38 may be installed between half sections 36 a, 36 b to prevent leakage of wellbore liquids into the gas filled cavities. To do so, a gland 40 may be formed on one part to accept o-ring 38 and a seating surface 42 may be provided on the other part opposite the gland, against which the o-ring seals.

If the cavities are filled with a solid material and substantially not harmed or displaced by well fluids, the cavities can be exposed on the surface of the ball (FIG. 7). In such an embodiment, the body material 530 may be exposed on the surface to come into contact with the seat, but sometimes may not cover the entire outer surface with the filler 537 filling at least some spaces between the body material and being exposed on the surface of the ball.

The balls may be constructed by molding or milling or various other means. The balls can be formed in various sizes, as desired. Some common diameters include those ranging from 1 to 4 inches.

The multiple parts may be connected in various ways. In the illustrated embodiment of FIGS. 2 and 3, for example, the halves 36 a, 36 b are joined together for use by a threaded connection 44 a, 44 b. As shown, for example, one half can include a threaded rod 44 a and the other half can include a correspondingly positioned and sized female threaded box 44 b for accepted threaded insertion of threaded rod 44 a. The threaded connection can be modified, for example as shown in FIG. 7, a rod 446 with threaded ends 447 a, 447 b may connect between threaded connections 448 a, 448 b on two exterior body parts 436 a, 436 b. Of course, other connection methods may be employed, as desired, such as frictional engagement such as a snap connection, adhesives, welding including fusing, tacking, etc.

FIG. 4 shows another ball 212, which is similar to the ball of FIG. 2. Ball 212 is formed of a durable outer shell 230 of aluminum. The outer shell is formed in two halves 236 a, 236 b that are connected to form a spherical outer surface 212 a. The body halves are connected by a threaded connection 244 a, 244 b that surrounds cavity 232. The threaded connection includes a threaded rod 244 a and a threaded box 244 b that are incorporated in the outer wall between wall 234 forming cavity 232 and outer surface 212 a. For example, the threaded box 244 b has threads formed on its inner facing surface and the opposite thickness of the wall of the threaded box is the outer surface 212 a of the ball. This maximizes the surface area of the threads and reinforces the walls, by providing thickness and an overlap for threading purposes adjacent the interface of the two halves. Cavity 232 is, therefore, fully open, defined by substantially cylindrical or substantially spherical walls, a portion of which is formed in each half.

While ball 212 may have a low specific gravity filler that is solid in form, in this illustration it has a gas filler in cavity 232. In this case, the gas may be air or nitrogen and may be pressurized above ambient. For example, the gas filler may be nitrogen pressurized to about 500 to 3500 psi or 1000 to 3000 psi. To seal the cavity against leakage, o-ring 238 is positioned in a gland 240 on the end of threaded rod 244 a that is pressed against a seating surface 242 when the ball halves are threaded together. Another o-ring 250 is positioned to encircle threaded rod 244 a and seal against the inner facing surface of box 244 b. The two o-rings offer enhanced redundancy as o-ring 238 provides a face style seal and o-ring 250 offers a piston-style seal.

FIGS. 5 and 6 show balls 312, 412, respectively, that are similar to the ball of FIG. 2, but each have a non-fluidic filler.

FIGS. 5 a and 5 b show a spherical ball 312 that has an outer shell 330 formed of durable materials (i.e. aluminum, steel, ceramic, etc.) and a lighter, composite filler 337 in the center. The ball has the performance of a solid ball, but the filler reduces the specific gravity of the ball over a solid aluminum ball. Filler 337 adds resiliency to the ball and takes compressive force that is transferred from the tool's seat to the aluminum shell, to avoid a crushing failure.

Ball 312 is formed as two halves formed with spherical surfaces that can be secured together to form a substantially spherical outer surface 312 a. The half spherical portions of filler 337 may each be secured by adhesive within their half outer shell parts of body material 330. Here, filler 337 forms threaded connection, rod 344 a and box 344 b, permits threaded connection of the two halves. Adhesive, for example epoxy, may also be applied at the threaded connection. Ball 312 can achieve a very low density, but is of high strength, able to withstand downhole rigors and high pressures P, but readily can circulate back to surface. Also, because of the low amount of aluminum in the construction, ball 312 is readily removed by milling, if it becomes stuck down hole.

Ball 412 of FIGS. 6 a and 6 b is similar to that of FIG. 5, but is manufactured in a different way. Ball 412 also has an outer shell 430 formed of durable materials such as aluminum and a lighter, composite filler 437 in a cavity entirely within the ball, encapsulated by the body material, when the ball is assembled.

Ball 412 is formed as two halves formed with two halves 436 a, 436 b of the shell having outer semi-spherical surfaces that can be secured together to form a substantially spherical outer surface 412 a. The halves 436 a, 436 b of the outer shell are held together by a threaded rod 446. As noted above, rod 446 has threaded ends 447 a, 447 b that connect between threaded connections 448 a, 448 b on two shell halves 436 a, 436 b. Rod 446 can be inserted through a hole 454 in filler 437 such that when threaded, the parts are all secured together. An epoxy or other glue is used to additionally secure the parts of the ball together so the ball doesn't come apart during use to actuate a downhole tool. The interfacing edges 436 a′, 436 b′ of the shell halves can be formed to overlap rather than fit in a butted way together. For example, one edge 436 a′ may be formed with an annular inner step and the other edge 436 b′ may be formed with an annular extension such that extension fits into the recess causing the edges to overlap when the shell halves are brought together. This adds strength at their connection.

With reference to FIGS. 7 a and 7 b, another ball 512 is shown that has multi-material construction to select for both durability and low specific gravity. Ball 512 has cavities defined by walls 534 that open onto the outer surface and when constructed filler 537 fills the cavities and forms a portion of the ball's outer surface 512 a. Ball 512 uses the more durable body material 530, in this case aluminum, as a “skeleton”. This skeleton framework takes the load of the ball against its seat and shields the composite from having to withstand the full load. The body material 530 includes a number of structural elements that extend regularly through the ball. They are substantially uniformly spaced apart through the ball such that regardless of how the ball lands on a seat, some portion of the body material 530 will be in contact with the seat and positioned to resist extrusion, crushing, etc. In this embodiment, the skeleton is a series of three intersecting plates, each one substantially following a great circle of the spherical shape of ball 512. For example, one plate substantially can extend through an equator of the ball, and two plates may be positioned substantially as spaced apart meridians. The edges 530 a of the plates are exposed on the outer surface of the ball when it is assembled and side walls of the plates form cavity walls 534. Thus, the edges 530 a of the aluminum plates support the ball against the seat. In this embodiment, the skeleton formed by body material 530 is constructed from a plurality of pieces of aluminum plate cut and assembled. Because filler 537, in this case polymeric composite with a specific gravity similar to water (about 0.8 to 1.1), is to be molded around the skeleton and fill the cavities, holes 539 are formed in the plates through which the filler can be joined cavity to cavity which assists with the stability of the ball.

In the ball of FIG. 7, filler 537 only has to hold the pressure and not the bearing load from the ball seat. Like the balls described above, the aluminum provides the ball with strength while the filler lowers the specific gravity of the ball over a fully aluminum ball and permits the ball to more readily flow back.

Balls such as those described above, can be used in various methods to actuate a downhole tool such as to expand a packer or to open or close a port. With reference to FIG. 1, according to one method, a downhole tool 14 with sliding sleeve 18 actuated by ball 12 may be positioned within a wellbore. The tool may, for example, be installed in a string and the string may be run into a wellbore and positioned at a location of interest.

Actuation ball 12 may be launched from above downhole tool 14, for example, from surface, such that it moves to land in seat 20 of the sliding sleeve valve. Sliding sleeve valve 18 may be driven thereby to operate the downhole tool (i.e. to open ports 22, communicate tubing pressure to a tool component, drive axial movement of a tool component, etc.). In one embodiment, for example, a wellbore fluid treatment such as stimulation including fracturing may be carried out after the ball actuates the tool to open ports 22.

In such a method, sliding sleeve valve 18 may be driven by a hydraulic pressure (arrow P) that can be generated above actuation ball 12 and sleeve, as the ball seals against seat 20. Considerable pressures can be achieved and the sleeve may be secured to only release and be driven by pressures above a selected value. Shear pins 24, collets, snap rings, etc. can be used to select the pressures at which a sleeve may move. As such, the actuation ball may be constructed to withstand such pressures against the seat without failure. For example, the ball may be selected to withstand such pressures while maintaining its integrity and position on the seat, for example, substantially without collapsing, extruding through the seat, shearing, etc. The ball for example may be constructed to have a strength to withstand pressures of 4000 to 12000 psi forcing the ball against the seat.

Thereafter, due to the nature of the actuation ball, circulation of fluids in the wellbore may be used to lift the actuation ball off the seat. Circulation may be by circulation of introduced wellbore fluids such as reverse circulation of drilling fluids or by actively lifting fluids from above, as by use of an up hole or surface pump. Alternately, the circulation of fluids may be generated by formation pressures such as production causing a reverse flow of introduced fluids or a flow of produced fluids.

The ball may be lifted off the seat and in one embodiment may be carried with the circulation of fluids back towards and perhaps all the way to surface.

Other balls may be useful for downhole actuations. For example, with reference to FIG. 8, a ball 610 is shown that is useful to actuate a tool 614, shown installed in a string 615. Tool 614 includes a sleeve 618 with a seat 620 and ball 612 can be employed to land in seat 620, create a seal with it and form a piston effect such that applied pressure P can move the sleeve to open ports 622 or otherwise create an effect.

The ball of FIG. 8 is another example, of a ball formed by use of multiple materials and having an irregular shape. Ball 610 also illustrates a configuration wherein the contact area on the ball that is intended for seating against the ball seat is defined, as opposed to being any part of the ball. The embodiment also includes an attachment 662 for the ball body 612 that facilitates location of the ball downhole.

Ball 610 includes a ball body 612 constructed from a plurality of materials: at least one that is strong enough to withstand wellbore rigors and pressure scenarios, termed herein the body material, and at least one that has a specific gravity less than 2.6, termed herein the filler 637. Ball 612 also has a defined seating area on its outer surface. Because the entirety of the ball is not intended to act as a possible seating surface, this allows a ball shape that isn't a complete sphere and thus the ball can be made of less material than a fully spherical ball having the same seat diameter. As shown, ball 612 has a less than fully spherical outer surface: it has a flattened end 660.

In the illustrated embodiment, a body material shell 630 is exposed on the outer surface of the ball, but only partially covers the ball. Ball 612 has a body with an outer surface that only a portion of which defines a seating surface with a substantially circular shape in section encircling an axis of the ball. Body material shell 630 is exposed on the outer surface of the ball at the seating area. In this embodiment, the body material forming seating surface has an outer shape only a portion of which is spherical. In particular, the body material 630 portion is a substantially annular member with a frusto-spherical shape.

The ball seating area, which in this embodiment is that area on which body material shell 630 is exposed, can be configured to suitably land and seal against the sealing area of seat 620 of tool 614, while the remainder of the ball body may not meet these requirements. For example, as shown one end 660 of the ball is flattened, such that the ball is only partly spherical (i.e. a portion of the sphere is removed).

In this embodiment, aluminum is employed for body material because it can accommodate the pressure induced force and load it into the seat without extruding into the seat like a softer material (i.e. a composite) might. As noted above, extrusion is generally to be avoided, as it may make the ball stick in the seat and can hinder the flow of produced fluids from below the ball seat. By utilizing aluminum as the outer shell extrusion is minimized. At the same time, aluminum is still relatively light (specific gravity of about 2.6) compared to steel. If this ball gets jammed somewhere down hole, it can be milled out easily because of the low volume of aluminum.

While ball body 612 could be entirely formed of the body material, the remainder of the ball body in this embodiment is formed of filler 637. In this embodiment, filler 637 is a polymeric solid having a specific gravity similar to water (0.5 to 1.5) and resistant to complete and/or immediate breakdown in wellbore conditions. Filler 637 forms the interior of the ball, attached to and filling within body material shell 630. Since ball defines a spherical curvature substantially only in that area defining the seating area, filler can be filled in and have various shapes, for example, forming the flattened end.

Because only a portion of ball 610 defines a seating area, ball 610 is configured to land in a particular orientation with the ball seating area on seat 620. For example, ball 610 is configured to ensure that the semi-spherical area, where body material shell 630 is exposed, lands on the seat, instead of an area where filler is exposed and instead of a non-spherical area such as end 660. In this embodiment, ball 612 has attached thereto an orientation member 662. In this embodiment, the orientation member is a flexible extension, in this embodiment including a flexible connector 664 carrying a fluid harnessing member 666. The orientation member is intended to pull the ball along and keep its axis x, and therefore seating area 630, that is concentric about axis x, oriented substantially parallel to, and possibly in line with, the long axis of the string, and therefore long axis x_(s) of tool 614. Orientation member 662 is attached at a connection site 668 on the front of the ball. The connection site can be positioned relative to the location of the body material to ensure that it lands against the seat properly. For example in the illustrated embodiment, connection site 668 is positioned at about the point through which ball axis x passes and is substantially concentric relative to seating area 630. Orientation member 662, through fluid harnessing member 666, pulls the ball 612 along ensuring that the connection site 668 leads movement of the ball toward seat 620. In one possible embodiment, connection site 668 may include a threaded collar secured to the ball that accepts a threaded fastener on the end of flexible connector 664.

Flexible connector 664 may take many forms. Flexible connector 664 may flex in at least one lateral direction about its long axis. In one embodiment, flexible connector 664 may flex in a number of directions about its long axis and, for example, may include elongate members that are fully flexible such as wire, cord, line, rope, string, chain, band, strap, cable, etc. Its flexibility allows the orientation member to readily pass through surface plumbing. For example, orientation member 662 can pass around elbows, through valves, etc. in the ball launching apparatus and other structures at surface.

Fluid harnessing member 666 may also take various forms to serve its intended purpose of pulling the ball along in the fluid flows toward and through tool 614. Fluid harnessing member 666 may, for example, include a finned member, a seal, a parachute, etc. Fluid harnessing member 666 can be formed to be conveyed in fluid pressure P. For example, the fluid harnessing member can be shaped to capture fluid pressure for conveyance thereof and/or can be sized to create a substantial seal against the seat or the string inner diameter ID. Fluid harnessing member 666 may be resilient, also able to pass though surface plumbing and to pass through seats such as seat 620.

In the illustrated embodiment, the fluid harnessing member includes a seal element that is sized to create a substantial plug in the inner diameter and pull the ball along by fluid pressure. The seal element includes a plurality of spaced apart circular seals 670 a, 670 b, which may be relatively flat (disc shaped, as shown) or concave (cup shaped), held together on a center stabilizing base 672. The seals 670 a, 670 b may be selected to have an outer diameter that creates a pressure harnessing blockage in the string and the inner diameter of the tool, for example, they may have outer diameters about the same as the inner diameter of the seat 620 (as shown) or even the ID of the string, such that the seals create a substantial seal with the constriction through which they pass and possible with the string inner wall. As illustrated in FIG. 8 b, the trailing end seal 670 a may have a diameter less than the leading end seal 670 b such that the leading end seal acts as a centralizer and the trailing one creates more of a seal.

Fluid harnessing member 666 may be selected to also work in the reverse for example to urge ball 610 up hole. Flat or bi-concave seals, that can harness fluid flows moving both upwardly and downwardly therepast, may work better for this than concave (cup shaped) seals. The member can urge the ball up hole by pulling or pushing the ball, according to its construction. For example, once the actuation effected by the ball is complete (i.e. once the stimulation is complete), the fluid harnessing member can help push the ball back to the surface. Flat seals may work better for this than concave shaped seals.

It will be appreciated that the flexible extension and the fluid harnessing member may have beneficial application even for balls with a one-component construction and/or fully spherical form. For example, the flexible extension and the harnessing member may be attached as a ball pulling device to pull small diameter balls through the string, since small diameter balls may not be as readily moveable by fluid pressure for example along horizontal sections of a well.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to those embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope consistent with the claims, wherein reference to an element in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 USC 112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or “step for”. 

1. An actuation ball for a downhole tool, the actuation ball comprising: a body having an outer surface defining a seating surface, the body having a specific gravity less than 2.6.
 2. The actuation ball of claim 1, wherein the body is formed of a body material and a filler, the filler having a specific gravity less than the body material.
 3. The actuation ball of claim 2, wherein the body material defines a cavity in which the filler is positioned.
 4. The actuation ball of claim 2, wherein the filler is a fluid including a gas and/or a liquid.
 5. The actuation ball of claim 4, wherein the fluid is pressurized.
 6. The actuation ball of claim 4, wherein the fluid is contained in a sealed cavity within the actuation ball.
 7. The actuation ball of claim 2, wherein the filler is a solid having a specific gravity of 0.5 to 1.5.
 8. The actuation ball of claim 7, wherein the filler is a polymer.
 9. The actuation ball of claim 1, wherein the cavity is enclosed by the body material.
 10. The actuation ball of claim 1, wherein the cavity opens to the outer surface.
 11. The actuation ball of claim 1, wherein the body material is aluminum and the cavity is enclosed by the body material.
 12. The actuation ball of claim 1, wherein the cavity is sealed against fluid migration.
 13. The actuation ball of claim 1, wherein the actuation ball has a first part and a second part threaded together at a threaded connection and wherein a cavity is defined between the first part and the second part in which a filler is contained.
 14. The actuation ball of claim 13, wherein the threaded connection encircles the cavity.
 15. The actuation ball of claim 1, further comprising a fluid harnessing member connected to the actuation ball, the fluid harnessing member formed to pull the actuation ball to the valve seat.
 16. The actuation ball of claim 1, further comprising an orientation member connected to the actuation ball, the orientation member formed to orient the actuation ball to land with the seating surface on the valve seat.
 17. A downhole tool assembly comprising: a tubular body; a sliding sleeve valve positioned within and axially moveable along a length of the tubular body, the sliding sleeve valve including a valve seat; and an actuation ball having an outer surface defining a seating surface, the actuation ball having a specific gravity less than 2.6.
 18. The downhole tool assembly of claim 17, wherein the actuation ball is spherical and the entire outer surface defines the seating surface.
 19. The downhole tool assembly of claim 17, wherein the actuation ball is spherical and only a portion of the outer surface defines the seating surface.
 20. The downhole tool assembly of claim 17, wherein the actuation ball is other than spherical and only a portion of the outer surface defines a seating surface.
 21. The downhole tool assembly of claim 17, wherein the actuation ball has attached an orientation member to orient the actuation ball to land with the seating surface on the valve seat.
 22. The downhole tool assembly of claim 17, wherein the actuation ball is filled with a pressurized gas.
 23. The downhole tool assembly of claim 17, wherein the actuation ball includes a shell and a filler within the shell that has a specific gravity less than the shell.
 24. The downhole tool assembly of claim 23, wherein the shell is aluminum.
 25. The downhole tool assembly of claim 17, further comprising a fluid harnessing member connected to the actuation ball, the fluid harnessing member formed to pull the actuation ball to the valve seat.
 26. A method for operating a downhole tool, the method comprising: providing a downhole tool including a tubular body and a sliding sleeve valve positioned within and axially moveable along a length of the tubular body, the sliding sleeve valve including a valve seat; providing an actuation ball having an outer surface defining a seating surface, the actuation ball having a specific gravity less than 2.6; positioning the downhole tool within a wellbore; launching the actuation ball from above the downhole tool such that the actuation ball moves to land in the valve seat of the sliding sleeve valve; driving the sliding sleeve valve to operate the downhole tool; and allowing circulation of the fluids in the wellbore to lift the actuation ball off the valve seat.
 27. The method of claim 26, wherein driving the sliding sleeve valve includes applying 4000 to 12000 psi on the actuation ball in the valve seat.
 28. The method of claim 26, wherein driving the sliding sleeve valve includes opening ports covered by the sliding sleeve valve and diverting treatment fluid through the ports and into the wellbore.
 29. The method of claim 26, wherein launching includes landing the seating surface of the actuation ball on the valve seat.
 30. The method of claim 26, wherein launching includes controlling movement of the actuation ball through the downhole tool to orient the actuation ball to land with only its seating surface on the valve seat.
 31. The method of claim 26, wherein launching includes harnessing fluid flow through the downhole tool to urge the actuation ball toward the downhole tool.
 32. The method of claim 26, wherein allowing circulation includes flow back of fluids.
 33. The method of claim 26, wherein allowing circulation includes flow of produced fluids.
 34. The method of claim 26, further comprising circulating the actuation ball to surface.
 35. An actuation ball for a downhole tool, the actuation ball comprising: a ball body having an outer surface defining a seating surface with a substantially circular shape in section encircling an axis of the actuation ball; and a flexible protrusion attached to the ball body and extending substantially coaxially relative to the seating surface.
 36. The actuation ball of claim 35, wherein the ball body is spherical and the entire outer surface defines the seating surface.
 37. The actuation ball of claim 35, wherein the ball body is spherical and only a portion of the outer surface defines the seating surface.
 38. The actuation ball of claim 35, wherein the ball body is other than spherical and only a portion of the outer surface defines a seating surface.
 39. The actuation ball of claim 35, wherein the flexible protrusion acts to orient the ball body to land with the seating surface on the valve seat.
 40. The actuation ball of claim 35, further comprising a fluid harnessing member connected by the flexible protrusion to the ball body, the fluid harnessing member formed to pull the ball body to the valve seat.
 41. A downhole tool assembly comprising: a tubular body; a sliding sleeve valve positioned within and axially moveable along a length of the tubular body, the sliding sleeve valve including a valve seat; an inner bore defined by an inner wall of the tubular body and of the sliding sleeve valve; and an actuation ball including a ball body and a flexible protrusion, the ball body having an outer surface defining a seating surface with a substantially circular shape in section encircling an axis of the actuation ball, and the flexible protrusion extending from the ball body substantially coaxially relative to the seating surface, the flexible protrusion acting to orient the seating surface to land in the valve seat.
 42. The downhole tool assembly of claim 41, wherein the ball body is spherical and the entire outer surface defines the seating surface.
 43. The downhole tool assembly of claim 41, wherein the ball body is spherical and only a portion of the outer surface defines the seating surface.
 44. The downhole tool assembly of claim 41, wherein the ball body is other than spherical and only a portion of the outer surface defines a seating surface.
 45. The downhole tool assembly of claim 41, wherein the flexible protrusion acts to orient the ball body to land with the seating surface on the valve seat.
 46. The downhole tool assembly of claim 41, further comprising a fluid harnessing member connected by the flexible protrusion to the ball body, the fluid harnessing member formed to pull the ball body to the valve seat.
 47. A method for operating a downhole tool, the method comprising: providing a downhole tool including a tubular body; a sliding sleeve valve positioned within and axially moveable along a length of the tubular body, the sliding sleeve valve including a valve seat; and an inner bore defined by an inner wall of the tubular body and of the sliding sleeve valve; providing an actuation ball including a ball body and a flexible protrusion, the ball body having an outer surface defining a seating surface with a substantially circular shape in section encircling an axis of the actuation ball, and the flexible protrusion extending from the ball body substantially coaxially relative to the seating surface; launching the actuation ball from above the downhole tool such that the actuation ball moves through the inner bore and the ball body lands in the valve seat of the sliding sleeve valve, the protrusion acting to orient the seating surface to land in the valve seat; and driving the sliding sleeve valve to operate the downhole tool.
 48. The method of claim 47, wherein driving the sliding sleeve valve includes applying 4000 to 12000 psi on the ball body in the valve seat.
 49. The method of claim 47, wherein driving the sliding sleeve valve includes opening ports covered by the sliding sleeve valve and diverting treatment fluid through the ports and into the wellbore.
 50. The method of claim 47, wherein launching includes moving the actuation ball through surface piping.
 51. The method of claim 47, wherein launching includes landing the seating surface of the ball body on the valve seat.
 52. The method of claim 47, further comprising allowing circulation of fluids up through the valve seat to lift the actuation ball off the valve seat.
 53. The method of claim 52, wherein allowing circulation includes flow back of fluids.
 54. The method of claim 52, wherein allowing circulation includes flow of produced fluids.
 55. The method of claim 47, further comprising circulating the actuation ball to surface.
 56. The method of claim 47, wherein allowing circulation includes harnessing fluid flows in a fluid harnessing member to drive the fluid harnessing member against the ball body and pushing the ball body off the valve seat. 